rte States Patent [191
Loutfy et al.
[54]
[11]
4,410,606
[45]
Oct. 18, 1983
LOW TEMPERATURE THERMALLY
4,370,392
1/1983 Savinell et al. ..................... .. 429/51
REGENERATIVE ELECTROCHEMICAL
4,377,623
3/1983
Parker et al. ..................... .. 429/105
SYSTEM
[75] Inventors: Raouf O. Loutfy, Tucson, Ariz.;
OTHER PUBLICATIONS
Alan P. Brown, Bolingbrook; Neng-
Hempel, Encyclopedia of Electric Chemistry, p. 619,
Ping Yao, Clarendon Hills, both of
ll].
1964.
Foster et al., J. of Metals, pp. 23-28, Jul. 1970.
_
.
[73] Assignee: The United States of America as rep-
.
.
.
t
R
‘lzgiig?yfidvmiclesiirégngggmc Chem“ 0 and
.
_
who
resented by the U'S' Department of
lwarnoto, iiijév of Photography (Japan) pp 278-282
Energy, Washington, D.C.
1967
’
'
’
’
'
‘
’
[21] Appl. No.: 370,639
[22] Filed;
Apr. 21, 1982
Primary Examiner—M. J. Andrews
Attorney, Agent, or Firm——Robert J. Fisher; William
[51]
Int. Cl.3 ............................................ .. HUIM 8/18
[52]
US. Cl. ...................................... .. 429/17; 429/20;
Lohff; Richard G_ Besha
[58]
429/105; 429/ 106; 429/ 108
Field of Search ..................... .. 429/ 17, 20, 50, 51,
[56]
429/ 105, 106, 108, 120
References Cited
ABSTRACT
A thermally regenerative electrochemical system in
eluding an electrochemical cell with two water-based
electrolytes separated by an ion exchange membrane, at
least one of the electrolytes containing a complexing
us PATENT DOCUMENTS
963,980
-
[57]
7/1910 Basset .................................. .. 429/20
agent and a Salt Ofa multivalent m?tal Whose respective
2,700,063
1/1955 Maneke ....... ..
429/149
order of potentials for a pair of its redox couples is
3,253,955
5/ 1966 clampitt et al- -
429/106
reversible by a change in the amount of the complexing
agent in the electrolyte, the complexing agent being
429/105
removable by dlstillation to cause the reversal.
22%“ Ct 31‘ '
,
,
4,192,910
C
........... ..
-
3/1980 Frosch at al. '
4,215,182
7/1980
4,292,378
9/1981 Krumpelt et al. .................. .. 429/15
Ang et al.
I267
.........
. . . ..
~
~
429/15
18 Claims, 8 Drawing Figures
/| 2 5
l
CH3CN
I 14
r
I I6
__ _
_
+
—— —
0.5 CuSO4
|.5 CH3CN
— ——
0.5 011504
- - q~|24
-
_
l
_.
l
0.25 0112504
CH3CN
O- 5 Cu °
\I I0
- -
I18 /
_ : .-
(2 1
V
I '2
\ 120
0. 5 0112504
CH CN
3
(I28
L122
0.25 Cu2SO4
CH3CN
US. Patent
Oct. 18, 1983
Sheet 1018
,_
4,410,606
CU++/CU+
5C0
E°,mV
300
I00
I00
300
g/l CH3CN
FIG. I
500
US. Patent
05¢. 18, 1983
Sheet 2 of 8‘
4,410,606
2|
I M CuSO4,
/
0.5 M cusog, /23
5 M CHBCN
0.5 M Cu°
I : l /22
ELCTRHOMIA
l
20/
I
118
I6/
I
\[O
O? m $32234’
A
0.5 M cusoq,
0.5 M Cu°
|.0 M CuSO4
5 M CH3CN
“28
l
:0 M cus04, /50
3 M CHaCN
US. Patent
ELCTROHMIA
‘THERMAL
0%. 18, 1983
Sheet 4 0f 8
4
IO M 01504,
c
5.0 M CH3“;
Cu'504, 0.5 Cu
80/
84;
90
y
0.5 M 0,2504,
5.0 M CH3CN
7
/ss
'-5 M Q1304
A
CH3CN
W
O-5 M @504,
0.5 M Cu°
92
/
L5 M CuSO4,
3.0 M CHBCN
I00
)
94
- %
a
ELCTRHOMIA
/|02
|.0 M 01504
5.0 M CH3CN
LO M CuSO4,
5.0 M CHsCN
|.0 M CuSO4,
0.5 M Cu°
7
US. Patent
00¢. 18, 1983
4,410,606
Sheet 5 of 8
20'
S7EYFICT0NMY,
2
4
6
CH3CNlCu+ RATIO
FIG. 5_
8
-
IO
U.S. Patent
Oct. 18, 1983
Sheet 7 of8
4,410,606
_
_
_
_
_
_
0%Qm06o.~o._oh9wo.»
NEF#5CU1mZz6o
US‘, Patent
0C8. 18, 1983
Sheet 8 of 8
4,410,606
~08
‘7
—O.5
54; ‘g_}Cu+/Cu°
_
Cu++/Cu+
—O.2
COPPER ELECTRODE
V-WlTHOUT STIRRING
O-WITH STIRRING
PLATINUM ELECTRODE
O-WITHOUT STIRRING
El-WITH STIRRING
l
l
l
l
l
L0
2.0
3.0
4.0
5.0
CURRENT DENSITY, mA/cmz
J
6.0
1
4,410,606
LOW TEMPERATURE THERMALLY
REGENERATIVE ELECTROCHEMICAL SYSTEM
2
system which does not require distillation of the metal
salt in the electrolytes. An additional object of the in
vention is a ‘thermally regenerative electrochemical
system. Yet another object of the invention is a ther
CONTRACTUAL ORIGIN OF THE INVENTION 5 mally regenerative‘electrochemical system in which the
regeneration temperature is below about 400° C. and
The US. Government has rights in this invention
preferably below 200° C.
pursuant to Contract No. W-3l-l09-ENG-38 between
the US. Department of Energy and the University of
SUMMARY OF THE INVENTION
Chicago representing Argonne National Laboratory.
Brie?y, the invention is directed to a regenerative
BACKGROUND OF THE INVENTION
This invention relates to an electrochemical system
utilizing an electrochemical cell and more particularly
to a thermally regenerative electrochemical system
electrochemical system in which regeneration of one or
more electrolytes is carried out at a temperature below
about 400° C. and preferably allow about 200° C. An
utilizing one or more electrochemical cells having wa
system utilizes one or more water-based electrolytes
containing a salt of a multivalent metal whose respec
tive order of potentials for ?rst and second redox cou
ter-based electrolytes containing salts of a multivalent
metal whose respective order of potentials for a pair of
its redox couples is reversible.
Thermally regenerative electrochemical systems
have some similarities to secondary batteries except that
the regeneration of the electrochemically active elec
trode reactants is accomplished thermally rather than
electrically. They may also be considered as devices to
convert or upgrade thermal energy to electrical energy
and advantageously include chemical storage means for
storing the energy until needed for electrical purposes.
Previously, thermally regenerative electrochemical
systems have been characterized by a number of limita
tions. In some systems, the regeneration has involved
the chemical decomposition of the reaction products to
produce the initial reactants as disclosed in US. Pat.
Nos. 3,536,530 and 936,980. Other systems havebeen
regenerated by the distillation of a salt to provide two
electrolytes of differing concentrations as in US. Pat.
No. 4,292,378. Photoelectric devices have also been
utilized to produce electricity to electrically generate
electrolytes at lower temperatures but this has been
other separate and important characteristic is that the
ples in water is reversed by the addition of a complexing
agent in an amount sufficient to cause the reversal. The
inventive system includes at least one electrochemical
’ cell including a pair of compartments with one or both
containing water-based electrolytes in contact with
associated electrodes and with at least one of the elec
trolytes containing a salt of the above described multi
valent metal and the complexing agent.
In the operation of the electrochemical cell, both of
the initial electrolytes become changed in composition
and form other electrolytes, with the metal salt associ
ated with the complexing agent in the one electrolyte
being changed to a more stable form in a subsequent or
third electrolyte. In a subsequent distillation step, the
complexing agent is removed to a low value causing a
reversal in vpotentials and a subsequent conversion of the
electrolyte to form one of the initial electrolytes. The
removed complexing agent is added to another electro
lyte derived from the initial electrolytes to form another
of the initial electrolytes. With this system, the thermal
limited by the cost and limited power associated with
step is carried out to remove at least a portion of the
these devices.
Particularly with some systems associated with the 40 complexing agent and does not require the removal by
distillation of the metal salt or the chemical decomposi
chemical decomposition of the reaction products, the
tion of the salt or the use of excessive temperature.
regeneration temperatures, energy requirements and
corrosive conditions have been substantial. In many
BRIEF DESCRIPTION OF THE DRAWINGS
instances, the regeneration temperatures have been at
In
the drawings,
least about 500° C. and often in excess of 500° C. In US. 45
FIG.
1 is a graph showing the change in potentials for
Pat. No. 3,536,530, the temperature of regeneration to
copper redox couples ~with respect to concentration of
form the initial chemical reactants is about 550° C. For
CH3CN in an aqueous solution.
a lithium hydride system as described in “The Encyclo
pedia of Electrochemistry”, Hampel (ed.), 1964, p. 619,
the regeneration temperature is about 900°—l200° C.
Since the cost of operating these regenerative electro
FIG. 2 is a schematic of one embodiment of the in
vention.
FIG. 3 is a schematic of a second embodiment of the
chemical systems is dependent on the cost of the energy
to regenerate the initial electrolytes for the electro
chemical cell, attention has been directed to lower cost
invention.
temperatures have usually been below those required
for many regenerative systems.
Example I.
FIG. 4 is a schematic of a third embodiment of the
invention.
FIG. 5 is a graph showing efficiency versus
energy sources. One convenient source is heat available 55
I CH3CN/Cu+ratio.
from low grade heat sources such as solar collectors or
FIG. 6 is a schematic of a fourth embodiment of the
from industrial operations which provide heat at tem~
invention.
peratures below 400° C. and often below about 200° C.
FIG. 7 is a graph of voltage versus current density for
While these sources of heat have cost advantages, the
Accordingly, one object of this invention is a new
regenerative electrochemical system with advantages
FIG. 8 is a graph of voltage versus current density for
Example II.
DETAILED DESCRIPTION OF THE
over those previously known. Another object is a re:
INVENTION
generative electrochemical systemvin which regenera 65
The
electrochemical
system of the invention for con~
tive energy isv not utilized to decompose the reaction
verting thermal energy to electrical energy includes an
products to reform the initial electrolytes. A second
electrochemical cell for storing the energy in chemical
object of the invention is a regenerative electrochemical
4,410,606
3
form and converting it to electrical energy as required.
The cell includes ?rst and second electrodes and two
4
with the formula RCN where R is a hydrocarbon with
l-3 carbon atoms; organic amides of the formula
compartments separated by an ion exchange member
and containing ?rst and second water-based electrolytes
in contact with the associated electrodes. At least one of 5
the electrolytes contains a complexing agent and a salt
of a multivalent metal whose respective order of poten
tials for ?rst and second redox couples in water are
reversed by the addition of the above complexing agent
in an amount suf?cient to cause the reversal. In the
operation of the cell, both electrolytes are changed in
composition with the electrolyte resulting from the one
electrolyte containing the complexing agent being iden
ti?ed as a third electrolyte.
In order to regenerate one or both of the original
electrolytes, regeneration means are provided including
means for thermally removing at least a portion of the
complexing agent from at least the third electrolyte to
reverse the order of the potentials causing the composi
R3
where R1 is a hydrocarbon with 1-2 carbon atoms and
R2 and R3 are hydrocarbons with l-3 carbon atoms; and
organic nitrates with the formula R4NO3 where R4 is a
hydrocarbon of 1-3 carbon atoms, and preferably the
?rst two compositions.
The suf?cient amounts of each complexing agent to
cause the desired reversal may be determined in a con
ventional manner from available stability data and data
on potentials associated with Cu+and Cu++ ions for
each agent.
tion to change to a more stable form resulting in a fourth
In the operation of the cell, the original electrolytes
electrolyte. The complexing agent is added to a ?fth
electrolyte derived from one of the electrolytes identi
?ed with operation of the cell, with the resulting elec
are changed in composition. To illustrate, an aqueous
will form Cu(CH3CN)2+. In the other electrolyte, a
trolyte forming the original ?rst or second electrolyte.
source of Cu0 in contact with an aqueous solution of
solution of CuSO4 with the complexing agent CH3CN
As illustrated in FIG. 2, the cell is constructed with 25 CuSO4 will form additional quantities of CuSO4. In
another embodiment, a source of Cu" in the presence of
two compartments containing the electrolytes and an
Cu2SO4 and CH3CN will form additional quantities of
electrode in contact with the appropriate electrolyte.
At least one and preferably both electrolytes are water
Cu2SO4 while CuSO4 with CH3CN in the other original
based and contain a salt of a multivalent metal charac
electrolyte will form Cu(CI-I,3CN)2+.
terized by at least two redox couples CHI/C" and
C"/C"—l with the respective potentials in water revers
ible by the addition of a complexing agent. Advanta
trolytes in the cell to eventually form one or both of the
geously, the metal salt is a copper salt and may include
copper sulfate, nitrate, acetate or other saltof an acid
which does not strongly complex with the copper salt
as with the complex of I-ICl and CuCl. Illustrative of the
potentials for the copper redox couples as illustrated in
FIG. 1 are the following values (vs NHE) in water in
the absence and presence of CH3CN.
Aqueous
Cu++/Cu+
Cu+/Cu"
Complexing Medium (CH3CN)
0.17 V
0.52 V
Cu'l""/Cu+
Cu+/Cu°
0.65 V
0.05 V
As indicated, the order of the potentials is reversed by
the addition of a complexing agent which is added in an
amount suf?cient to reverse the order. For CH3CN, this
amount is in the order of about 2.5-3.0 moles of com
plexing agent per mole of cuprous salt. From the above
potentials, the reaction occurring in the cell is governed
by the equation
Regeneration means is utilized with the changed elec
original electrolytes. Advantageously, the regeneration
means includes means for thermally removing at least a
portion of the complexing agent to reverse the order of
the potentials. To illustrate, distillation of a solution of
Cu2SO4 and CH3CN will remove a portion of CH3CN
suf?cient to reverse the potentials and form CuSO4 and
Cu" as a result of the above equation. The CH3CN is
added to the other changed electrolyte containing
CuSO4 to form a solution of CuSO4 and CH3CN.
CuSO4 remains unchanged since no source of Cu” is
present to complete the reaction.
In one embodiment of the invention illustrated in
FIG. 2, an electrochemical cell 10 is illustrated with
45 electrodes 12 and 14 in compartments 16 and 18 respec
tively containing electrolytes 20 and 22 as indicated in
boxes 21'and 23. As illustrated, electrolyte 20 is com
posed of an aqueous solution of one molar CuSO4 and a
3 molar CH3CN. Sulfuric acid is also present to im
prove the conductivity of ‘the solution. The second
electrolyte is composed of an aqueous solution of 0.5
molar CuSO4 and a source of elemental copper suf?
cient to form a Cu+ or Cu++ concentration of 0.5
molar. In the operation of the cell 10, the ?rst electro
lyte 20 is changed in composition to form a third elec
with the cupric ion (Cu++) being more stable in the
trolyte 24 containing 0.5 molar Cu2SO4 with the
noncomplexed aqueous system and with the cuprous
CH3CN unchanged. The second electrolyte 22 is
ion (Cu+) being more stable in the complexed system.
changed to a ?fth electrolyte 26 with the elemental
Further characteristics of the potentials for CuSO4/
copper being changed to CuSO4 to form a one molar
Cu2SO4 and Cu2SO4/Cu couples are shown in A. J.
Parker, et al., Aust. J. Chem. 30, 1661 (1977). It is to be 60 solution. As illustrated, at least a portion of the com
plexing agent CH3CN is distilled at a temperature
understood that Cu2SO4, when complexed with
below about 200° C. from the third electrolyte 24 and
CH3CN, represents the Cu+ion in the form
transferred to electrolyte 26 to form a sixth electrolyte
Cu3°(CH3CN)2.
_
30. From the distillation, the third electrolyte 24 is con
Since the complexing agent is subsequently removed
by distillation or other means utilizing thermal energy, 65 verted to a fourth electrolyte 28 which is composed of
0.5 CuSO4 and a source of elemental copper. The resul
the complexing agents are preferably characterized by
boiling temperatures between about 30°—90° C. Suitable
complexing agents with these characteristics are nitriles
tant electrolytes 28 and 30 represent both of the original
electrolytes 22 and 20 for cell 10.
5
4,410,606
In a second embodiment as illustrated in FIG. 3, cell
40 includes electrodes 42 and 44 inserted in compart
ments 46 and 48 respectively containing a ?rst electro
lyte 50 and a second electrolyte 52. In the operation of
cell 40, a third electrolyte 54 is formed from ?rst elec
trolyte 50 and represents an oxidation of elemental cop
per to its cuprous form. Also, ?fth electrolyte 56 is
derived from second electrolyte 52 and represents a
reduction in electrolyte 52 to a cuprous form. As illus
‘6
The following examples are provided for illustrative
purposes and are not intended to be restrictive as to
scope of the invention:
EXAMPLES I-II
An electrochemical cell was constructed of two glass
compartments separated by a ?ne porosity-?tted glass
disc. The anode was a copper rod of about 0.08 cm2 in
diameter with the electrolyte in the associated compart
‘ trated, the electrolyte 54 is distilled to remove at least a
ment being an aqueous solution of about 0.625 M CH2.
portion of CH3CN to form fourth electrolyte 58 com
S04, 0.75 M H2SO4 and 3.5 M CH3CN. The cathode
posed of CuSO4 and a source of Cu". The elemental
copper is transferred to a ?fth electrolyte 56 to form
was carbon in one test and platinum in a second test.
The associated electrolyte was an aqueous solution of
sixth electrolyte 62 while the complexing agent with
about 0.25 M CuSO4, 0.5 M H2SO4 and 3.5 M CH3CN.
With the cell at a substantially charged condition, the
electrode potential of the anode and cathode were mea
drawn from the third electrolyte 54 is added to electro
lyte 58 to form seventh electrolyte 64 containing
CuSO4 and CH3CN. In this embodiment, both the com
plexing agent and elemental copper are selectively re
moved from certain electrolytes and added to other
electrolytes to form the initial electrolytes 52 and 50.
In a third embodiment as illustrated in FIG. 4, the
sured as a function of an imposed discharging current
with the results being shown in FIG. 7 for the carbon
cathode and in FIG. 8 for the platinum cathode. As
indicated by the data, the copper anode shows very
little polarization with increasing current density. For
each cathode some polarization is exhibited and is sig
initial electrolytes are ?rst and second electrolytes 80
ni?cantly affected by stirring of the electrolyte. The
and 82 contained in compartments 84 and 86 in cell 78.
In the operation of the cell 78, a third electrolyte 88 and 25 data further indicate that the cell voltages are in the
order of 0.5-0.55 volts at discharge current densities of
?fth electrolyte 90 are formed. As illustrated, the com
up to about 5-6 mA-cm-Z.
plexing agent CH3CN is removed by distillation from
The foregoing description of embodiments of the
electrolyte 88 to- form fourth electrolyte 92 with the
invention has been presented for purposes of illustration
complexing agent being transferred to electrolyte 90 to
form sixth electrolyte 94. While electrolytes 92 and 94 30 and description. It is not intended to be exhaustive or to
limit the invention to the precise form disclosed, and
represent similar compositions to the ‘original electro
lytes 82 and 80, the concentrations are made more iden
obviously many modi?cations and variations are possi
tical through the use of cell 96 with compartments 98
and 100 in which electrolyte 92 is changed to electro
ble in light of the above teaching.
lyte 102 and electrolyte 94 is changed to electrolyte 104.
A portion of the complexing agent is removed from
electrolyte 104 to form electrolyte 106 while the com
plexing agent is added to electrolyte 102 to form elec
trolyte 108 with electrolytes 106 and 108 forming the
original electrolytes 80 and 82.
FIG. 5 represents a graph in which the ef?ciency of
the overall system is plotted versus the molar ratio of
complexing agent to cuprous ion concentration. As
indicated in the graph, the ef?ciency reaches a maxi
mum at a ratio of about 2.5-3.0. Other tests were con
ducted and reveal that a ratio of approximately 2.5 is the
value at which the respective order of potentials for the
redox couples changes from one direction to another
although the relationship does not involve an abrupt
change.
In FIG. 6, a diagram is provided to show the overall
operation of the system with a distillation unit. As illus
trated, cell 110 is operated to generate power for load
112 with supply tanks 114 and 116 providing sources of LII 5
electrolytes for compartments 118 and 120, respec
tively. The electrolyte resulting from the operation of
the cell is withdrawn from compartment 120 and trans
ferred via conduit 122 to distillation unit 124 where the
complexing agent CH3CN is removed overhead by
conduit 125 to be mixed with a source of CuSO4 from
conduit 126 to form the electrolyte for tank 114. The
source of CuSO4 is obtained from the bottoms of distil
The embodiments of the invention in which an inclu
sive property or privilege is claimed are de?ned as
follows:
1. An electrochemical system comprising an electro
chemical cell having ?rst and second electrodes and
two compartments separated by an ion exchange mem
brane and containing ?rst and second water-based elec
trolytes in respective contact with said ?rst and second
electrodes, at least one of the ?rst and second electro
lytes containing a complexing agent and a salt of a mul
tivalent metal whose respective order of potentials for
?rst and second redox couples in water are reversed by
the addition of said complexing agent in an amount
suf?cient to cause said reversal, said agent being present
in at least said amount, said one electrolyte being con
verted to a third electrolyte in the operation of the cell,
and means for regenerating said ?rst or second electro
lyte from said third electrolyte in a sequence of steps,
said regeneration means including thermal means for
removing at least a portion of said complexing agent
from said third electrolyte to reverse the order of said
potentials and form a fourth electrolyte and means for
adding said complexing agent to a ?fth electrolyte de
rived from said electrolytes in said cell to form said ?rst
or second electrolyte.
2. The system of claim 1 wherein said regenerating
means includes a second electrochemical cell and a
second thermal means.
3. The system of claim 1 wherein said second electro
lyte contains a salt of said multivalent metal and said
mental copper by conduit 128 which is returned to be 65 multivalent metal is copper.
4. The system of claim 1 wherein one of said compart
mixed with the electrolyte withdrawn by conduit 127
ments contains a source of the elemental form of said
from compartment 118 and then transferred to tank 116
metal.
to form the electrolyte for compartment 120.
lation tower 124 which also includes a source of ele
4,410,606
7
5. The system of claim‘3 wherein said thermal means
includes distillation means operative at temperatures
below about 200° C.
6. The system of claim 5 wherein said metal is copper,
where R4 is a hydrocarbon with l-3 carbon atoms.
14. A method of converting thermal energy to electri
cal energy comprising the steps of providing ‘an electro
chemical cell having ?rst and second electrodes and
two compartments separated by an ion exchange mem
brane and containing ?rst and second water-based elec
said complexing agent is CH3CN and said amount is
above about 2.5 moles of complexing agent per mole of
the cuprous ion.
'
i
8
'
trolytes in respective contact with said ?rst and second
7. The system of claims wherein said ‘complexing
agent has a boiling temperature between about 30°-90°
electrodes, at least one of the ?rst and second electro
lytes containing a complexing agent and a salt of a mul
C.
tivalent metal whose respective order of potentials for
_.
8. The system of claim 7 wherein said ?rst and second
?rst and second redox couples in water are reversed by
the addition of said complexing agent in an amount
electrolytes each contain said complexing agent.
suf?cient to cause said reversal, said agent being present
in at least said amount, operating said cell to produce
9. The system vof claim 6 wherein said salt of copper
is a sulfate, nitrate or acetate salt.
electrical energy and convert one electrolyte to a third
10. The system of claim 8 wherein said ?rst and sec
electrolytefand regenerating said ?rst or second elec
trolyte from said third electrolyte ‘including the steps of
thermally removing at least a portion of said complex
ond electrolytes include an acid which does not form a
complex with said salt.
'
11. The system of claim 7 wherein the complexing
agent is RCN where R is hydrocarbon with >1-3 carbon
ing agent from said third electrolyte to a value below
said amount to reverse the order of said potentials to
atoms.
form a fourth electrolyte and adding said complexing
agent to a?fth electrolyte derived from said electro
12. The system of claim 7 wherein the complexing
agent is
- ‘
25
lytes in said cell to form said ?rst or second electrolyte.
‘15. The method of claim 14 wherein said regenerating
step includes the step‘ of operating a second electro
chemical cell after said removal of said complexing
‘
R3
agent.
-
1
16. The method of claim 15 wherein said thermal
removal step includes distilling the third electrolyte to
remove said complexing agent.
where R1 is hydrocarbon with 1-2 carbon atoms and R2
and R3 are each hydrocarbons with 1-3 carbon atoms.
> '17. The method of claim 16 wherein said distillation
13._ The system of claim 7 wherein the complexing
step is carried out at a temperature below'about 200° C.
18. The method of claim 17 wherein said multivalent
35 metal is copper;
‘ ' agent is
._
45
55
65
*
a:
s